1. Field of the Invention
This invention relates to dot printers, and more particularly to a dot printer head.
2. Description of the Prior Art
In conventional dot printer heads, rear ends of needles are connected to electromagnets arranged radially. The needles are bent and slidably inserted in a plurality of needle guides, and the top ends of the needles are aligned at equal pitch. In this construction, the needle and needle guide are liable to abrasion due to the sliding action of the bent needle. In order to reduce the abrasion, the amount by which the needle is bent must be reduced and the bending load must be reduced. If a ring connecting the rear ends of the needles is used for this purpose, the inner portion of an armature in the electromagnet used to strike the rear end of an associated needle may interfere with other adjacent armatures. Therefore, the reduction of needle bending amount by this technique is limited. Since the rear end of the needle extends in both the axial direction, and the radial direction and since the rear end of the needle is displaced laterally about the needle guide at the rearmost portion as a fulcrum, the armature and the needle cap (which is fixed at rear end of the needle) must have large contacting area therebetween. This results in enlargement of the ring connecting the rear ends of the needles so as to prevent interference between the adjacent armatures, which further increases the difficulty of reducing the bending amount of the needle. If the area of the top end of the armature is increased, the amount of inertia is greatly increased, and the electromagnet must be made large. Such increase in the size of the electromagnet means that high-speed performance cannot be expected and that consumption of power increases.
In order to reduce lateral displacement of the needle, the distance between the needle guide at the rearmost portion and the needle cap may be reduced, and the spring used to urge the needle in the reset direction may have a large spring constant. However, use of a spring having a large spring constant makes the needle fly, whereby good printing is not obtained.